Add derive DeriveIntoActiveModel and IntoActiveValue trait

[tqwewe]

Creates a new derive macro DeriveIntoActiveModel for implementing IntoActiveModel on structs. This is useful for creating your own struct with only partial fields of a model, for example an insert struct, or update struct.

// Define regular model as usual
#[derive(Clone, Debug, PartialEq, DeriveModel, DeriveActiveModel)]
#[sea_orm(table_name = "users")]
pub struct Model {
    pub id: Uuid,
    pub created_at: DateTimeWithTimeZone,
    pub updated_at: DateTimeWithTimeZone,
    pub email: String,
    pub password: String,
    pub full_name: Option<String>,
    pub phone: Option<String>,
}

// Create a new struct with some fields omitted
#[derive(DeriveIntoActiveModel)]
pub struct NewUser {
    // id, created_at and updated_at are omitted from this struct, and will always be `ActiveValue::unset`
    pub email: String,
    pub password: String,
    pub full_name: String, // Full name is usually optional, but it can be required here
    pub phone: Option<String>, // Option implements `IntoActiveValue`, and when `None` will be `unset`
}

#[derive(DeriveIntoActiveModel)]
pub struct UpdateUser {
    pub phone: Option<Option<String>>, // Option<Option<T>> allows for Some(None) to update the column to be NULL
}

fn main() {
    let new_user = NewUser {
        email: "someone@domain.com".to_string(),
        password: "test".to_string(),
        full_name: "John Doe".to_string(),
        phone: None,
    };
    
    let active_model = new_user.into_active_model();
    // active_model can now be used in queries...
}

Additionally, an attribute active_model is available in case your active model struct has a custom name.

#[derive(DeriveIntoActiveModel)]
#[sea_orm(active_model = MyActiveModel)]
pub struct NewProduct {
    // ...
}

[tyt2y3]

Is it better if the active_model attribute is a string?
I discovered it is not possible to have :: in the value

Can't compile

#[derive(DeriveIntoActiveModel)]
#[sea_orm(active_model = my_mod::MyActiveModel)]
pub struct NewProduct {
    // ...
}

Should work

#[derive(DeriveIntoActiveModel)]
#[sea_orm(active_model = "my_mod::MyActiveModel")]
pub struct NewProduct {
    // ...
}

[tqwewe]

Is it better if the active_model attribute is a string?
I discovered it is not possible to have :: in the value

Can't compile

#[derive(DeriveIntoActiveModel)]
#[sea_orm(active_model = my_mod::MyActiveModel)]
pub struct NewProduct {
    // ...
}

Should work

#[derive(DeriveIntoActiveModel)]
#[sea_orm(active_model = "my_mod::MyActiveModel")]
pub struct NewProduct {
    // ...
}

Oh I wasn't aware that wouldn't work. I guess it's better to use a string then. I can create another PR to change this if you'd like?

[tyt2y3]

Oh I wasn't aware that wouldn't work. I guess it's better to use a string then. I can create another PR to change this if you'd like?

Sure, that'd be appreciated!
(And it is more in line with DeriveRelation)